Technical Tips

Water Quality in Hydroponics Applications: MyronLMeters.com

Posted by 7 Jan, 2014

TweetWHAT IS HYDROPONICS? “A technique of growing plants in nutrient solution”. Hydroponics literally means water-working or water-activation. It is a cultivation technique for growing plants in highly oxygenated, nutrient enriched water, rather than soil. The nutrient solution and its management are the cornerstone for a successful hydroponics system. The function of a hydroponics nutrient solution […]

WHAT IS HYDROPONICS?
“A technique of growing plants in nutrient solution”. Hydroponics literally means water-working or water-activation. It is a cultivation technique for growing plants in highly oxygenated, nutrient enriched water, rather than soil.

The nutrient solution and its management are the cornerstone for a successful hydroponics system. The function of a hydroponics nutrient solution is to supply the plant roots with water, oxygen and essential mineral elements in soluble form.

In soil, biological decomposition breaks down organic matter into basic nutrients that plants feed on. Water dissolves these nutrients which allows uptake by the roots. For a plant to receive a well balanced diet, everything in the soil must be in perfect balance.

Depending on the product, there are approximately seventeen (17) required elements for proper growth. For growth of higher plants, nine of these elements (macro nutrients) carbons, hydrogen, oxygen, sulfur, phosphorus, calcium, magnesium, potassium, and nitrogen are required in relatively large amounts. The remaining eight elements (micro-nutrients or trace elements) iron, zinc, copper, manganese, boron, chlorine, cobalt, and molybdenum are needed in only minute amounts.

To support a plant in a system, an insert medium like fiber or leca, may be used to anchor the roots. These mediums are designed to be very porous for excellent retention of air and water for healthy plants-roots to breathe! With the proper light exposure, nutrients, pH and EC/TDS measurements, plants will grow many times faster, bigger and healthier.

WHAT IS pH? WHY IS IT IMPORTANT?
pH, means “potential hydrogen” ion concentration (commonly referred to as acidity or alkalinity) in a particular medium, such as water, soil, etc. All elements have a specific solubility pH range. This means that mineral elements can become more available for plant uptake within certain pH ranges. The scale of pH is 0 to 14, 14 is the highest for alkalinity, 7 is neutral, and 0 is the highest acidity. It is well documented that growing media pH is critical to successful plant growth. This is especially true for soilless mixes and hydroponics.

Extreme pH conditions such as very low pH (below pH 4.5) and very high pH (above pH 9) can cause damage to plant roots and limit or kill production.

WHAT IS ELECTRICAL CONDUCTIVITY (EC) OR TOTAL DISSOLVED SOLIDS (TDS)? WHY IS IT IMPORTANT?
EC [displayed in either microsiemens (μS) or micromhos (μM)] is the measurement of the nutrient solutions ability to conduct an electrical current. In hydroponics the conductivity (EC) is most commonly expressed in an equivalent Total Dissolved Solids (TDS) value. The unit of measurement for TDS is parts per million (ppm). Pure water (deionized water) is actually an insulator — it does not conduct electricity. It is the conductive substances (or ionized salts) dissolved in the water that determine how conductive the solution is. With few exceptions, when there is a greater concentration of nutrients, the electrical current will flow faster, and when there is a lower concentration, the current will flow slower.

This is because the quantity of dissolved solids in the nutrient solution is directly proportional to the conductivity. Thus, by measuring the EC, one can determine how strong or weak the concentration of the nutrient solution is.

HOW IS EC CONVERTED TO PPM OF TDS?
Myron L meters use a complex equation that exactly matches the true TDS of the solution being tested. While other instrument manufacturers use a “fixed” factor (easier and less costly to manufacture) to “estimate” the TDS from electrical conductivity. As you can see in the following examples a fixed factor of, for example .5 is far off the mark.

solution table

 

 

 

 

 

TEMPERATURE COMPENSATION (TC), WHY IS IT IMPORTANT?
Without Temperature Compensation (TC), instrumentation measuring waters/nutrients would be indicating different values at differing temperatures. TC standardizes the readings at the international standard of 25°C / 77°F. With proper TC all readings will be repeatable at differing temperatures and may be correlated. All Myron L meters use advanced TC circuitry and equations to give you the best TC correction available.

CALIBRATION STANDARD SOLUTIONS
Clearly the “BEST” choice when calibrating instrumentation for controlling water and nutrients in Hydroponics, Greenhouses and Agricultural applications is the “442™” natural water standard.

This standard developed over 40 years ago closely matches the composition of natural water. The “442” refers to the combination of salts with deionized water to make the standard: 40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride. Since its development, it has become the world’s most accepted natural water standard. All HYDROPONICS Instruments from the Myron L Company are calibrated using this standard.

For truly accurate and repeatable readings for your Hydroponic applications, use Myron L meters and “442” Standard Solutions.

All instrumentation, pH buffers and EC/TDS standards are available HERE at MyronLMeters.com.

bottom table

Categories : Application Advice, Technical Tips

Horticulture Applications: MyronLMeters.com

Posted by 13 Nov, 2013

Tweet                    WHY ARE TESTS SO IMPORTANT? Modern growing practices include scientific evaluations of soil, water, fertilizers, diseases, etc. While some tests are best performed by a laboratory, others can be easily conducted on location, saving time and money. Three tests in particular, EC, pH, and ALKALINITY, […]

The Myron L Ag-6/pH

 

 

 

 

 

 

 

 

 

 

WHY ARE TESTS SO IMPORTANT?

Modern growing practices include scientific evaluations of soil, water, fertilizers, diseases, etc. While some tests are best performed by a laboratory, others can be easily conducted on location, saving time and money. Three tests in particular, EC, pH, and ALKALINITY, can reveal valuable information about water quality, soil salinity, and fertilizer concentration. Our portable AGRI-METERS™ provide you with a simple, fast, and accurate means of testing these parameters.

WHAT IS ELECTRICAL CONDUCTIVITY (EC)?

EC is the measurement of a solution’s ability to conduct an electrical current. For horticultural applications, the unit of measure is often expressed as millimhos. Absolutely pure water is actually a poor electrical conductor. It is the substances (or electrolytes) dissolved in the water which determine how conductive the solution will be.

Therefore, EC can be an excellent indicator of:

1. Water quality

2. Soil salinity

3. Fertilizer concentration

EC AND WATER QUALITY

The quality of irrigation water is one of the most critical factors influencing your growing operation. It is important to have a complete water analysis performed on a regular basis. Environmental conditions such as drought, changing seasons, heavy rainfall, etc., can cause the concentrations of dissolved salts in your water to vary significantly. These dissolved salts (i.e. calcium, sodium, etc.) can directly affect your plants’ health and, over time, render even the best soil useless.

You can monitor your overall water quality by testing its electrical conductivity with an AGRI-METER™. The higher the EC, the more salts are dissolved in your water. By comparing your EC with previous readings, you can tell if any dramatic changes have occurred. Nutrient deficiencies are possible when water is too pure (low EC) or if the relative concentrations of some nutrients are unbalanced (i.e. calcium/magnesium). On the other hand, nutrient toxicities or osmotic interferences can also be traced to water quality. Water EC of even one millimho or below can cause problems. High EC readings of more than two millimhos can suggest serious problems, and special cultural procedures may be required.

EC AND SOIL SALINITY

“Water, water, everywhere, but not a drop to drink” is an old saying that applies to your plants when the soil salinity becomes too high. Salts from irrigation water and fertilizers tend to accumulate in your soil or growing media. High soil salinity disrupts the normal osmotic balance in plant roots. In severe cases a plant will become dehydrated even when the soil is wet. Symptoms of high soil salinity include: leaf chlorosis and necrosis, leaf drop, root death, nutrient deficiency symptoms, and wilting. All too often these symptoms are not recognized as being caused by soluble salts in the growing media. Sampling your soil and testing the EC of an extract can reveal important information about a soil’s suitability and your crop’s health.

Samples should be representative of different depths and locations. An easy-to-perform extract method is available with a Soil Test Kit. A 2:1 or 5:1 water-to-soil ratio is made using the small vials provided. Soil test labs often use a method that calls for testing the EC of an extract from a thicker slurry. Therefore, you may see higher soil EC readings from a lab. It is important to standardize your sampling, extract, and testing methods. This will keep the difference between lab and field testing to a predictable factor.

EC AND FERTILIZER CONCENTRATION

You know how important fertilizer is to your plants, but do you know how accurate your fertilizer dosage is? Relying on traditional proportional methods is risky to plants and can waste expensive fertilizer. Improperly mixed fertilizer or a malfunctioning injector can lead to less than optimal results or even a disastrous loss of crops. Many fertilizer companies now recommend using a simple EC test to verify correct fertilizer concentrations. Many growers check their fertilizer injectors on a weekly basis, or they use a continuous EC monitor.

Fertilizer companies and suppliers often can provide a chart relating EC to parts per million concentrations of their various fertilizers. If one is not available for the fertilizer you use, carefully make some stock solutions at commonly used strengths and test their EC. This will give you a data base for future reference.

To test the EC of fertilizer solutions:

  1. Test and record the EC of the water to be mixed with the fertilizer.
  2. Test the conductivity of the fertilizer and water mixture.
  3. Subtract the water conductivity determined in #1 above.
  4. The resulting figure is an accurate indication of how much fertilizer is present (a higher conductivity means more fertilizer).

Important note: Interpretation of results differs from formula to formula and even among manufacturers of the same formula. Obtain the proper EC charts from the fertilizer company.

Myron L Meters sells both portable and inline instrumentation to make your fertilizer monitoring easy. Myron L AGRI-METERS™, AG-5 and AG6/PH, TH1, waterproof TECHPRO II™ models TP1, TPH1 and TH1, and waterproof ULTRAMETER II™ models 4P and 6PFCEare handheld instruments which make fertilizer testing as simple as filling a cup and pushing a button.

The Myron L 750 Series II™ EC Monitor/controllers can be used to continuously monitor your fertilizer concentration. Their “alarm” relay circuit acts as a safeguard in a fertilizer injection system or even as the main controller for your injector. A 0-10 VDC output for chart recorders or PLC (SCADA) input is standard on all monitor/controller models.

IMPORTANCE OF pH

pH, the measure of acidity or basicity, should be included in any soil or water test. It is well documented that growing media pH is critical to successful plant growth. This is especially true for new soilless mixes and hydroponics. pH affects the roots’ ability to absorb many plant nutrients. Examples include iron and manganese, which are insoluble at high pHs and toxic at low pHs. pH also directly affects the health of necessary micro-organisms in soil.

The effectiveness of pesticides and growth regulators can be severely limited by spray water pH that is either too low or too high.

ALKALINITY

It is important to note that testing the pH of irrigation water reveals only part of the story. Testing water alkalinity (bicarbonates and carbonates) is much more important than generally recognized. Alkalinity dictates how much influence the water’s pH will have on your soil and nutrient availability. In addition, alkalinity has a very great effect on the ease or difficulty of reducing the pH of water.

 

 

Categories : Application Advice, Case Studies & Application Stories

Basic Maintenance of a Myron L Analog Meter: MyronLMeters.com

Posted by 5 Nov, 2013

Tweet                 BATTERY CHECK Most Myron L analog meters have a battery indicator glow light visible through the small hole on the lower right-hand corner of the meter face plate. If this light fails to glow when the black button is pressed, replace both batteries. BATTERY REPLACEMENT To […]

AH-DS-EP-10-2T

 

 

 

 

 

 

 

 

BATTERY CHECK

Most Myron L analog meters have a battery indicator glow light visible through the small hole on the lower right-hand corner of the meter face plate. If this light fails to glow when the black button is pressed, replace both batteries.

BATTERY REPLACEMENT
To replace the batteries detach the battery connectors. Pull on the plastic straps to remove the batteries. Replace with fresh zinc carbon or alkaline 9 volt batteries. Reinsert the plastic straps to secure batteries.

CELL CUP
Self-conditioning of the built-in electrodes occurs each time the button is pressed with a sample in the cell cup. This ensures consistent results each time. With some samples a small downward swing of the pointer is a result of this conditioning action. This action is powerful and removes normal films of oil and dirt. However, if very dirty samples – particularly scaling types – are allowed to dry in the cell cup, a film will build up. This film reduces accuracy. When there are visible films of oil, dirt, or scale in the cell cup or on the electrodes, scrub them lightly with a small brush and household cleanser. Rinse out the cleanser, and the meter is ready for accurate measurements. pH SENSOR The unique pH electrode in your pDS meter is a nonrefillable combination type which features a porous Teflon* liquid junction (covered by U.S. Patent No. 4128468). It should never be allowed to dry out (see pH MEASUREMENT). If it does, the sensor can sometimes be renewed by soaking in a saturated potassium chloride (KCI) solution for several days. “Drifting” can be caused by a film on the sensor bulb. Use a liquid cleaner such as Windex™ or fantastik™ to clean it. The sensor buIb is very thin and delicate. Excessive pressure during cleaning may break it. Leaving high pH (alkaline) solutions in contact with the pH sensor for long periods of time can damage it. Rinsing such liquids from the pH compartment and moistening it with 4 buffer or tap water will extend its useful life. Samples containing chlorine, sulphur, or ammonia can “poison” any pH electrode. If it is necessary to measure the pH of any such sample, thoroughly rinse the pH sensor with clean water immediately after taking the measurement. Any sample element which will reduce (add an electron to) silver, such as cyanide, will attack the reference electrode. Replacement sensors are available from MyronLMeters.com. *™ DuPont Company

WATER INSIDE THE METER
Your Myron L meter is a rugged instrument and will withstand water exposure around its cell, meter movement, and switches. However, care should be taken to keep water from leaking in around the bottom cover. It is not sealed (to prevent condensation from forming). If the water is relatively clean (i.e., tap water or better), and there are only a few drops inside the meter, dry it as described below. Large amounts of water, or corrosive or very dirty solutions will almost certainly damage the meter movement or electronics. Such meters should be returned to the Myron L Company for repair.

To dry your meter:
1. Shake excess water out of the inside of the meter.
2. Dab the exposed surface dry with an absorbent cloth or tissue. Avoid pushing any water into the Calibration Controls or the switches.
3. Air dry the meter in a warm area with the bottom cover off. Allow several hours for thorough drying. If the water entered through a leak in the case or cell, or if the instrument shows erratic readings or other unusual behavior, return it for servicing.

For more on repairs and maintenance, or to download an operations manual, please visit us HERE.

 

Categories : Care and Maintenance, Product Updates, Technical Tips

Myron L Meters for Hydroponics: MyronLMeters.com

Posted by 5 Sep, 2013

TweetFeatures • Handheld meters measure TDS and/or pH • Monitor measures TDS • All instruments are easy to operate and calibrate • High degree of accuracy • Immediate results • Kit comes with solutions required to calibrate • Temperature compensated readings TDS Monitoring The nutrient solution and its management are the foundation of a successful […]

Features

• Handheld meters measure TDS and/or pH
• Monitor measures TDS
• All instruments are easy to operate and calibrate
• High degree of accuracy
• Immediate results
• Kit comes with solutions required to calibrate
• Temperature compensated readings

TDS Monitoring

The nutrient solution and its management are the foundation of a successful hydroponics system. The function of a hydroponics nutrient solution is to supply the plant roots with water, oxygen and essential mineral elements in soluble form.

A test of the Total Dissolved Solids (TDS) using the DS Meter or pDS Meter or continuous monitoring with the HYDRO-STIK gives the grower accurate measurements of the concentration of nutrients in solution. If the concentration drops below the optimum level required to sustain and grow the plants, add more nutrient- rich solution until the desired concentration level is achieved. This prevents haphazard dosing and wasted solution, which minimizes costs to the grower.

pH Monitoring

pH of the nutrient solution is also critical to successful plant growth. All elements have a specific solubility pH range. This means that mineral elements dissolve and can become more concentrated in solution within certain pH ranges. Roots absorb only the dissolved nutrients, so this is critical to plant growth.
The TH1H and the pDS Meter quickly and easily measure pH.

Monitoring the addition of a pH balancing solution with the proper meter lets the grower precisely adjust the pH level.

Beyond affecting nutrient availability, extremely low or high pH can even damage or kill plants.

All Myron L TDS and pH meters give lab-accurate results in the field.

All Myron L meters use advanced Temperature Compensation (TC) circuitry and equations to give you the best TC correction available.

Ultrapen PT2 pH and Temperature Pen

Ultrapen PT2 pH and Temperature Pen

Ultrapen PT1 TDS Pen

Ultrapen PT1 TDS Pen

T6/pH TDS and pH Meter

T6/pH TDS and pH Meter

Techpro II - TPH1 TDS, pH, Conductivity, Temperature

Techpro II – TPH1 TDS, pH, Conductivity, Temperature

PSTK Soil Test Kit

PSTK Soil Test Kit

 

 

Categories : Application Advice

Measurement of Free Chlorine Disinfecting Power in a Handheld Instrument: MyronLMeters.com

Posted by 4 Sep, 2013

TweetINTRODUCTION AND OVERVIEW The most popular germicide used in water treatment is chlorine, which kills bacteria by way of its power as an oxidizing agent. Chlorine is used not only as a primary disinfectant at the beginning of the treatment process, but also at the end to establish a residual level of disinfection during distribution […]

INTRODUCTION AND OVERVIEW
The most popular germicide used in water treatment is chlorine, which kills bacteria by way of its power as an oxidizing agent. Chlorine is used not only as a primary disinfectant at the beginning of the treatment process, but also at the end to establish a residual level of disinfection during distribution as a guard against future contamination.
The most popular field test instruments and test systems for judging the level of residual chlorine, also called Free Available Chlorine (FAC), are based on colorimetric methods whereby dyeing agents are added to the sample being tested. These additives react to FAC causing a color change in the test sample. While they may detect the presence of FAC, they do not directly measure the electrochemical characteristic of FAC responsible for its disinfecting power: Oxidation-Reduction Potential (ORP). They give an incomplete and sometimes misleading picture of sanitizing strength. These methods have gained industry-wide acceptance. Unfortunately, so have the weaknesses and inaccuracies inherent to them.
The Free Chlorine Equivalent (FCE) feature avoids these pitfalls by directly measuring ORP, the germ-killing property of chlorine and other oxidizing germicides. It displays both the ORP reading (in millivolts DC) for the sample being tested as well as an equivalent free chlorine concentration in familiar ppm (parts per million). It accounts for the very significant effect of changing pH on chlorine sanitizing power; can be used for other types of oxidizing germicides and; will track the effect of additives, such as cyanuric acid, that degrade chlorine effectivity without changing the actual concentration of free available chlorine present.

CHLORINATION BASICS
NaOCl, common household bleach (5.3% NaOCl by weight) is the most popular chlorinating agent in use today. When added to water it hydrolyzes as:
NaOCl + H2O  HOCl + Na+ + OH-
Sodium hypochlorite Water Hypochlorous acid Sodium ion Hydroxide

Additionally, some of the HOCl dissociates into H+ and OCl-:
HOCl  H+ + OCl-
Hypochlorous acid hydrogen ion hypochlorite ion

Both HOCl and OCl- are oxidants and effective germicides, particularly against bacteria and viruses, with some effectivity against protozoa and endospores. HOCl is the stronger and more effective of the two species.

Chlorine Demand
When chlorine is added to water, not all of it is available to act against future contaminates. Some is deactivated by sunlight. Some is consumed by reactions with other chemicals in the water or by out-gassing as Cl2. More commonly, it is used up directly by disinfection of the pathogens already
present in the water or by combining with ammonia (NH3) and ammonium (NH4+) (byproducts of living bacteria) to form various chloramine compounds.
Chlorine Demand is the amount of chlorine in solution that is used up or inactivated after a period of time and therefore not available as a germicide.

Free Available Chlorine
Free Available Chlorine (FAC) is any residual chlorine that is available, after the chlorine demand is met, to react with new sources of bacteria or other contaminants. According to White’s Handbook of Chlorination and Alternative Disinfectants, 5th edition, this is the sum of the all of the chemical species that contain a chlorine atom in the 0 or +1 oxidation state and are not combined with ammonia or other organic nitrogen. Some species of FAC that might be present are:
• Molecular chlorine: Cl2
• Hypochlorous acid: HOCl
• Hypochlorite: OCl-
• Trichoride: Cl3- a complex formed by molecular chlorine and the chloride ions (Cl-)

In most applications the two most common species of free chlorine will be HOCl and OCl-. Much of the Cl2 will hydrolyze into HOCl that, depending on pH, will stay in the form of HOCl or partially dissociate into OCl-. Cl3- is very unstable and only trace amounts will be present. In fact, in most of the literature describing chlorination and the monitoring of chlorine residuals, free chlorine is considered to be the sum of HOCl and OCl-.

Chlorine dioxide, ClO2, is another chlorine derivative used in some public water supplies as a disinfectant. It is 10 times more soluble in water than chlorine and doesn’t hydrolyze into HOCl or dissociate into OCl-. In the absence of oxidizable substances and in the presence of hydroxyl ions, ClO2 will dissolve in water then decompose slowly forming chlorite ions (ClO2-) and chlorate ions (ClO3-), both of which are oxidants fitting White’s definition of free chlorine.

All other things being stable (temperature, pH, etc.), ORP values are related to FAC concentration levels. As the concentration of FAC in solution rises or falls, regardless of the species (HOCl, OCl-, ClO2-, ClO3- or Cl3-), the ORP value does, as well.

Combined and Total Chlorine
The term Combined Chlorine usually refers to residual chlorine that has combined with NH3 or NH4+ to form monochloramine (NH2Cl),
dichloramine (NHCl2) or trichloramine (NCl3). Combined chlorine is noteworthy here because chloramines are oxidizers and are used as germicides, though their reduction potential and therefore, disinfecting power is lower than other species of chlorine, such as HOCl, OCl- or ClO2.
Total chlorine is the sum of FAC and Combined Chlorine. An advantage of ORP-based systems is
that the aggregate ORP value of the water being tested includes the ORP levels contributed by all oxidizers, including chloramines. Therefore, ORP- based measurements automatically take into account Total Chlorine and can readily be used to judge total sanitizing strength.

Chlorine as an Oxidizing Germicide
Both HOCl and OCl- are oxidants and as such their effectivity as germicides can be determined using
ORP measurements. The cytoplasm and proteins in the cell walls of many harmful microbes are negatively charged (they have extra electrons). Any oxidant that comes into contact with the organism will gain electrons at the expense of the proteins, denaturing those proteins and killing the organism.
When enough chlorine is added to water to reach an ORP value of 650mV to 700mV, bacteria such as E. coli and Salmonella can be killed after only 30 seconds of exposure. Many yeast species and fungi can be killed with exposure of only a few minutes. Even ORP values of 350mV to 500mV indicate effective levels of chlorination with satisfactory microbe kill levels, although exposure times are required to be in the minutes rather than seconds.

The Importance of pH
pH significantly changes relative effectiveness of chlorine as a disinfectant. Different species of chlorine ions are more prevalent at different pH levels. Under typical water treatment conditions in the pH range 6–9, HOCl and OCl- are the main chlorine species. Depending on pH level, the ratio of these two free chlorine species changes.

Figure 1

Figure 1 – Distribution of Free Chlorine Species in Aqueous Solutions

Figure 1 shows that chlorine hydrolysis into HOCl is almost complete at pH ≤ 4. Dissociation of HOCl into OCl- begins around 5.5 pH and increases dramatically thereafter2. This is important because HOCl and OCl- do not have the same effectivity as disinfectants. HOCl can be 80-100% more effective as a disinfectant than OCl-. Optimum disinfection occurs at pH 5 to 6.5 where HOCl is the prevailing species of free chlorine present. As pH rises above that level, the ratio shifts towards being primarily OCl-. At pH 7.5 the ratio is about even. When the pH value rises to 8 or higher, OCl- is the dominant species. Therefore, assuming the concentration of Cl2 species is constant, the higher the pH of the solution rises above 5.5, the lower the oxidation capability and disinfecting power of the FAC.

The bottom line is knowing the concentration of FAC ions in a solution without taking pH into account can give an incomplete and sometimes incorrect picture of disinfecting power.

WHY A CHANGE IS NEEDED

The Problem with Colorimetric Testing
First and foremost, colorimetric tests only report how much chlorine is present, and as we saw in the previous section, knowing “how much” is not at all the same as knowing “how effective”.
Colorimeters and DPD kits add a reagent or several reagents to the water being tested that causes a color change representing the amount of FAC in water. In fact, they fundamentally change the chemistry of the water just to get an easy measurement.

The most obvious change is related to pH. The typical reagent/dye used in the process forces the pH of the sample to a specific level, usually 6.5 pH and thus radically alters the HOCl to OCl- ratio. If the original sample was at a pH of 7.4 to 7.6 (suggested levels for pools and spas) about 50% of the FAC present would be in the form of HOCl. At a pH of 6.5 this ratio rises to nearly 90%. While the actual concentration of FAC may be correct, a fact entirely overlooked is that the FAC in the source water includes about 40% of the much weaker sanitizing OCl-.

If that were the only change being made to the chemistry of the sample, it would be severe enough.

Figure 2 shows the result of a comparison test made using a UV spectrophotometer on two samples of water. Both were taken from a master water sample containing 5 ppm Cl2 prepared using a closed system that ensured no other oxidants or interferants were present. One was processed using a colorimeter reagent according to its operator’s manual instructions. The other was left untreated.

Figure 2

Figure 2: Chemical Alteration of Chlorinated Water by Colorimeter Additives

UV spectrophotometric analysis shows how dramatically the chemistry of the sample was changed by the addition of the colorimeter’s coloring reagent.
• The shift in the center of the spike indicates that the species of chlorine present has been altered. What was OCl- is now some other chemical species.
• The amplitude of the spike demonstrates how severely the amount of chlorine has been amplified.
• The absorption spectra where OCl- used to be is significantly depressed.

Because the area of UV absorption spectra where any OCl- would appear is so depressed, it is clear that a radical alteration is taking place above and
beyond simply changing the pH. The “ppm” value reported for the chlorine content of the water seems to be converted to a single species whose
concentration is significantly higher than the original OCl- content.

Even assuming a linear relationship between this altered chemistry and the original FAC content of the water that might be factored into the final colorimetric measurement, by completely divorcing the measurement from the pH of the source water, any direct correlation to the reduction potential of the FAC present and, therefore, real disinfecting power, is lost.

ORP = DISINFECTING POWER
What is ORP?
ORP is the acronym for Oxidation Reduction (REDOX) Potential. It is a differential measurement of the mV potentials built up between two electrodes exposed to solutions containing oxidants and/or reductants. ORP describes the net magnitude and direction of the flow of electrons between pairs of chemical species, called REDOX pairs. In REDOX reactions, one chemical of the pair loses electrons while the other chemical gains electrons. The chemicals that acquire electrons are called the oxidants (HOCl, OCl-, ClO2, bromine, hydrogen peroxide, etc.). The chemicals that give up electrons are called the reductants (Li, Mg2+, Fe2+, Cr, etc.).

Oxidants acquire electrons through the process of reduction, i.e., they are reduced. Reductants lose their electrons through the process of oxidation, i.e., they become oxidized.

How is ORP Measured?
ORP sensors are basically two electrochemical half- cells: A measurement electrode in contact with the solution being measured and a reference electrode in contact with an isolated reservoir of highly concentrated salt solution. When the solution being measured has a high concentration of oxidizers, it accepts more electrons than it looses and the measurement electrode develops a higher electrical potential than the stable potential of the reference electrode. A voltmeter in line with the two electrodes will display this difference in electrical potential (reported in mV). Once the entire system reaches equilibrium, the resulting net potential difference represents the Oxidation Reduction Potential (ORP). A positive reading indicates an oxidizing solution, and a negative reading indicates a reducing solution. More positive or negative values mean the oxidants or reductants present are stronger, they are present in higher concentrations or both.

What Does ORP Measure?
Measuring ORP is the most direct way to determine the efficacy of oxidizing disinfectants in aqueous solutions. It measures the actual chemical mechanism by which oxidizers, like chlorine, kill bacteria and viruses. The higher the ORP value, the stronger the aggregate residual oxidizing power of the solution, the more aggressively the oxidants in it will take electrons from the cells of microbes and, therefore, the more efficiently and effectively any source of new microbial contamination will be neutralized.
Also, because ORP measures the total reduction potential of a solution, ORP measures the total efficacy of all oxidizing sanitizers in solution: hypochlorous acid, hypochlorite, monochloramine, dichloramine, hypobromous acid, ozone, peracetic acid, bromochlorodimethylhydantoin, etc.

Can ORP Replace Free Chlorine Measurements?
Yes.
When correlated with known disinfection control methods, measurements and bacterial plate counts, this type of measurement gives an accurate picture of the residual chlorine sanitizing activity reported as an empirical number that is not subject to visual interpretations. Solutions with certain ORP levels kill microbes at a certain rate. Period!
ORP was first studied at Harvard University in the 1930s as a method for measuring and monitoring microbial disinfection. It has been advocated as the best way to judge residual disinfecting power of chlorinated water by water quality experts since the 1960s. ORP has long been used in bathing waters as the only means for automatic chemical dosing. The World Health Organization (WHO) suggests an initial ORP value of between 680-720 mV for safe bathing water3 and ~800 mV for safe drinking water.
For the purpose of pretreatment screening to detect chlorine levels prior to contact with chlorine- sensitive RO membranes, some manufacturers of RO membranes and other water quality treatment equipment will also specify an ORP tolerance value for prescreening and influent control.

There are, however, applications where reporting residual disinfecting power in terms of FAC concentrations is preferred and sometimes required. While ORP measurements do not directly measure the concentration of FAC, they can be correlated to free chlorine levels in ppm. Variables such as pH and temperature must be accounted for or controlled. Interfering chemicals that might be present, such as other oxidants or reductants, must also be accounted for, or better yet, removed.

Once all these factors are known or controlled, ORP values can be linked to concentrations either by way of laboratory experimentation or via mathematical formulas like the Nernst Equation, an equation that describes the relationship between the electrode potential of a specific chemical in a solution and its concentration. In either case this is an often complex and laborious process … until now.

FCE = HANDHELD ORP ACCURACY
ORP Relevance in a Handheld Instrument
The Myron L Company has developed an innovative method for using ORP-based measurement to directly monitor the disinfecting power of free chlorine and report the result in both familiar ppm units as well as straight ORP mV values.

Myron L Company’s FCE function utilizes the accurate and reliable electronic design of Myron L Company’s instruments combined with simple one- button operation to make ORP-based chlorine measurement available in an easy-to-use, handheld field instrument. Other handheld instruments may measure ORP, but only a Myron L Company instrument equipped with FCE quickly correlates ORP and pH with FAC concentration. The FCE function also includes a predictive algorithm that extrapolates a final, stable ORP value of a solution without waiting out the long response time of the typical ORP sensor.

When the FCE function is active, the instrument display alternates between the Predicative ORP reading (mV) and the Free Chlorine Equivalent (FCE) concentration (ppm). Together these features combine to make ORP-based free chlorine measurement relevant in a handheld field instrument.

FCE – How and Why it Works
The Myron L Company FCE feature cross-references ORP values with pH levels to automatically arrive at a concentration value for FAC that reflects the effect of pH on the ratio of HOCl to OCl-. This correlation is derived from a series of experiments in which exact amounts of chlorine (in the form of laboratory grade bleach: 5% NaOCl; 95% H2O) were added to deionized water in a closed system, thus controlling and excluding possible interferants. By using both a pH measurement and an ORP measurement, FCE can determine the relative contributions of HOCl and OCl- to the final ORP value and factors them into a final concentration calculation.

Figure 3

Figure 3 – Sample Experimental Data Relating FAC ppm to ORP and pH

Similar experiments were performed using water to which precise amounts of calcium chloride (CaCl2) and sodium bicarbonate (NaHCO3) were added to slightly buffer the water. This allows the FC feature to correlate low ORP values to the typically low FAC concentrations of tap water after it has been in the municipal water system for several days.

FCE – pH Included, Not Ignored
Unlike other FAC test methods that ignore the effect of pH on sanitizing power by artificially forcing the pH of their test sample to a single value, Myron L Company’s FCE includes pH in its concentration calculation. This capability gives Myron L Company’s FCE the ability to compensate for the effect of the changing ratio of chlorine species as pH
changes, resulting in a FAC concentration value germane to the actual sanitizing power of the source water. OCl- is measured as OCl-, and HOCl is measured as HOCl. Those users who are primarily concerned with or who prefer free chlorine concentration levels have a reliable measurement that gives consistent and comparable results, reading to reading, without having to rigorously control or artificially manipulate the sample’s pH.

In addition, because the FCE function displays both the FAC concentration and a predicted, stable ORP value, the user can, by comparing these two values from successive measurements, track how ORP (and disinfecting power) falls as pH rises and how ORP rises as pH is lowered when concentration is constant.

FCE – Chemistry Measured, Not Altered
Both DPD kits and colorimeters may tell the user the FAC concentration of the sample in the test tube, but since the chemistry of that sample is quite different from the source water being analyzed, the results are imprecisely related to actual disinfection power.

DPD kits and colorimeters only imply true disinfecting power; they do not measure it, and that is, after all, the whole point of the exercise.

The Myron L Company FCE method avoids these pitfalls and inaccuracies. FCE measures the real, unaltered chemistry of source water, including moment-to-moment changes in that chemistry.
The following controlled study shows exactly how differently the two methods respond, particularly at the high end where the effects of changes in pH are the greatest. In this study measurements were made with a digital colorimeter and a Myron L Company Ultrameter II 6P equipped with FCE. The solutions tested were made with various known concentrations of NaOCl in deionized water. The water was heated to above 80°C to remove any CO2 and, therefore, avoid interference from REDOX reactions between HOCL, OCl- and carbonates (HCO3).

Table 1

Table 1 – Comparison of FCE to Digital Colorimeter

In this study as the pH rises and the ratio of OCl- to HOCL rises dramatically, the FCE is able to accurately track the changing concentration of FAC. The colorimeter’s results do not.

FCE – Handheld ORP Accuracy Without the ORP Delay
One of the challenges in implementing an ORP- based free chlorine measurement in a handheld field instrument is the sometimes lengthy response time of ORP sensors. It is not uncommon for an ORP sensor to take 12 to 15 minutes to arrive at a valid stable reading. In extreme cases, such as an older sensor in poor condition and measuring a complex solution with a very low ionic strength, the ORP measurement can take up to an hour to fully stabilize. Obviously, for a handheld instrument these are unacceptably long times.

The Myron L Company FCE function includes a pioneering feature that dramatically reduces the wait for stable ORP readings. This unique feature determines an extrapolated, final, stabilized ORP reading within 1 to 2 minutes rather than the typical 15 minutes or hours for other ORP systems.

The Predictive ORP feature’s calculations are based on a model of sensor behavior developed through a series of experiments that measured the response time of a representative sample of ORP sensors over a range of controlled chlorine concentrations. The results of this set of experiments revealed that the shape of the curve is very similar for various ORP levels differing only in the initial starting point and the final stabilized reading.

Figure 4

Figure 4 – Example of ORP Sensor Response Study

Using a proprietary curve-matching algorithm, the Predictive ORP feature determines what point along the typical sensor response curve a measurement occurred and extrapolates an appropriate final reading. This extrapolated value is used to calculate the FCE ppm value without having to wait for the sensor to stabilize and is also reported directly to the instrument’s display.

FCE – FLEXIBILITY FOR THE REAL WORLD
Another advantage of an ORP-based measurement such as the Myron L Company FCE feature is that, within the limits of its range, it can be used to measure the disinfection effectivity of ANY oxidizing germicide. Myron L Company FCE measurement can be used with non-bleach oxidants, such as chloramines or even non-chlorine oxidants, such as peracetic acid, bromine or iodine.
The Predictive ORP value displayed when the FCE function is active is directly relevant for monitoring and controlling the sanitizing effectivity of oxidizing sanitizers besides HOCl and OCl-.
While the concentration values reported by the FCE function will not be absolutely correct for non-FAC oxidants, since they are based on a HOCl / OCl- model, FCE can still be an effective tool for monitoring relative changes in concentration levels. For absolute accuracy a correlative study should be performed to relate concentration levels of the oxidant in question to the ORP values displayed by the Predictive ORP feature and ppm values output by the FCE.

FCE = Effective Chloramine Control
A perfect example of the Myron L Company FCE ‘s flexibility is the use of chloramines as a germicide.
Chloramines are formed when chlorine (Cl2) and ammonia (NH3) come into contact, forming three different inorganic chemicals: monochloramine (NH2Cl), dichloramine (NHCl2) and trichloramine (NCl3). In some applications chloramines are considered an unavoidable side effect of the chlorination process; however, because they are also oxidants, there are other applications where they are used as the primary disinfectant in water treatment.

Chloramines are effective at killing bacteria and other microorganisms, but because their relative ORP levels are lower compared to HOCl or OCl- at the same concentrations, the disinfection process is slower.

Table 2

Table 2 – Electrode Potentials of Chloramines vs. HOCl

On the plus side, chloramines last longer than HOCl and OCl- (as long as 23 days in some cases), impart a less strong flavor or smell and their sanitizing
strength is not appreciably affected by changing pH.

Most importantly, chloramine-based water treatment methods produce much fewer hazardous byproducts. The US EPA limits the total concentration of the four chief hazardous byproducts of chlorination (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water. To avoid exceeding theses standards, many municipal water districts prefer using chloramine rather than chlorine.

The following table shows typical ORP values for various concentrations of monochloramine (NH2Cl).

Table 3

Table 3 – ORP Values for NH2Cl in Pure Water

When ORP levels of NH2Cl approach and exceed 500 mV, effective sanitization occurs with exposure times of 20 to 30 minutes. This is more than adequate for municipal water treatment.
Since Myron L Company FCE function bases its measurement on ORP, it presents an empirical, easy to interpret measurement, both in terms of the Predictive ORP display and the FAC equivalent concentration, allowing the user to monitor falling chloramine concentration as disinfection proceeds.

FCE and Cyanuric Acid (CYA) – Don’t Guess. Know!
Outdoor pool maintenance is a prime application where ORP-based chlorine measurement should be preferred. The use of chlorine to sanitize pools runs afoul of the fact that much of the chlorine added to an outdoor pool is deactivated by exposure to UV radiation in sunlight.

Cyanuric Acid (CYA) is often added to the pool water to “protect” FAC. In a typical pool at 7.6 pH about 50% of the FAC is OCl-, which reacts to UV radiation that passes through the Earth’s ozone layer (290nm). CYA combines with FAC to form N-chlorinated-cyanurates, which only react to UV radiation (215nm to 235nm) removed by the Earth’s ozone layer. Since N-chlorinated-cyanurates are also oxidizers, they also act as germicides. Unfortunately, they have much lower reduction potentials and, therefore, a much lower strength as a germicide.

Figure 5

Figure 5 – Effect of Cyanuric Acid on Chlorine ORP Values

Pool maintenance websites that advocate the use of cyanuric acid (not all of them do) often recommend levels of 40 to 80 ppm. Figure 5 shows how severely ORP and disinfecting power are affected by CYA.

The addition of only 20 ppm CYA decreases the pool water’s ORP 120 mV, reducing the effectivity of FAC from 1.5 ppm to an effectivity that is equivalent to only 0.3 ppm. Adding 40 ppm, or worse, 80 ppm, reduces sanitizing strength even more severely. This is definitely a case where more is not better.
A 1972 study on water chlorination showed that water treated with enough chlorine to kill 100% of the E. coli present in 3 minutes or less required almost 6 times as much chlorine be added for the same effect when 50 ppm of CYA was added.

Cyanuric acid beneficially affects pool chlorination by greatly reducing that portion of chlorine demand related to loss due to UV. Unfortunately, if you are using a colorimeter or DPD kit, it will tell you that your FAC concentration is unchanged and significantly misrepresent sanitizing strength
The Myron L Company FCE function’s ability to react to changes in ORP makes it an ideal tool for keeping track of how CYA affects residual sanitizing power when added to a chlorinated pool. The Predicative ORP display provides a direct and effective way to monitor changes in ORP values as CYA concentration increases. Because the FCE ppm
display reacts to changes in ORP and pH, it will reflect changes in the sanitizing strength as an “equivalent” or “effective” FAC concentration.

SUMMARY
Judging the true effectivity of chlorine as an oxidizing germicide requires more than just knowing how much chlorine is present. Changing pH or the addition of additives like cyanuric acid can radically alter the effectivity of the chlorine present. To accurately measure the effects of these issues requires a test method based on the precise measurement of ORP (the chemical characteristic directly responsible for killing microbes like bacteria and viruses) and cross-referenced to pH.

The Myron L Company FCE is the first measurement function that allows handheld, field instruments to integrate ORP and pH measurements into a system for monitoring the residual disinfecting power of free available chlorine in aqueous solutions.

• It provides an empirical measurement that does not require interpretation.
• It is not affected by water color or turbidity.
• It measures the true chemistry of the water, unaltered.
• It accounts for changes in pH.
• It reports the effects of CYA on disinfecting power.
• It can be used to monitor non-chlorine oxidants.

Myron L Meters features the Myron L FCE function in several instruments that read free chlorine – the Ultrameter II 6P, the Ultrameter III 9P, the PoolPro PS9 and PS6 models, and the
new Ultrapen PT4, soon to be released.

Categories : Science and Industry Updates, Technical Tips

pH Sensor Technical Reference: MyronLMeters.com

Posted by 3 Sep, 2013

Tweet What is pH? Definition: pH is the negative logarithm of hydrogen ion activity in a solution. The Concentration ratio of hydrogen ions (H+) and hydroxyl ions (OH-) determine the pH value of a solution. Any hydrogen activity will produce a 59.16 mV/ pH unit across the glass membrane. The measurement is expressed on a […]

pH Sensor
What is pH?

Definition: pH is the negative logarithm of hydrogen ion activity in a solution.

The Concentration ratio of hydrogen ions (H+) and hydroxyl ions (OH-) determine the pH value of a solution. Any hydrogen activity will produce a 59.16 mV/ pH unit across the glass membrane. The measurement is expressed on a scale of 0.0 to 14.0. Water with a pH of 7 is considered neutral (H+ ions = 10-7 and OH-
ions =10-7). A solution is considered acidic when the hydrogen ions (H+) exceed the hydroxyl ions (OH-), and a solution is considered an alkaline (base) when the hydroxyl ions (OH-) exceed Hydrogen ions (H+).

How is pH measured?
A pH instrument consists of three main components, refer to Figure 1.

1. The pH measuring cell: Hydrogen sensitive glass is blown onto the end of an inert glass stem.
A silver wire, treated with silver chloride (Ag/AgCl) is sealed inside the glass (cell) with a solution of potassium chloride saturated with Silver chloride.

The measuring solution has a neutral pH level of 7 or 0 mV. A properly hydrated glass sensor will produce a “Gel Layer” on the inside and outside of the glass membrane. The “Gel Layer” enables hydrogen ions to develop an electrical potential
across the pH glass sensor; a millivolt signal varies with hydrogen ion activity on the glass membrane while submerged in the solution being tested.

1. The Reference cell: A silver wire treated with silver chloride (Ag/AgCl) is sealed inside an inert glass housing (cell) with a solution of potassium chloride saturated with silver chloride. The inert glass prevents hydrogen ion activity from test solutions to influence the reference cells constant millivolt signal. The combination of the reference electrode silver- silver chloride wire, and the saturated potassium chloride solution develops a constant 199-millivolt reference signal. The millivolt signal produced inside the reference electrode does not vary as long as the chloride concentration remains constant. The reference voltage is used as a baseline to compare variations or changes in the solution being tested. The reference cell is in contact with the test solution through a reference junction that is commonly made of porous Teflon®*‚ ceramic, or a wick type material called a Pelon strip. This junction completes the measuring circuit of the pH sensor.

2. Display meter: When the pH sensor is placed in a solution, the pH-measuring cell develops a millivolt signal that reflects the hydrogen ion activity of the test solution. A high impedance meter accurately measures the small millivolt changes and displays the results in pH units on either an analog meter or digital display.

Temperature considerations:
The pH glass membrane is sensitive to the temperatures of solutions being tested. Prolonged use and/or exposure to temperatures (above 35°C) will accelerate the aging, and increase chemical attack
to the glass membrane which will shorten the overall service life of the sensor.

ELEVATED TEMPERATURES WILL SHORTEN THE SERVICE LIFE OF A pH SENSOR.

Increase temperatures also decreases the impedance of the glass membrane. The decrease of the impedance affects the millivolt output of glass membrane.
Temperature changes close to neutral (pH 7) usually do not affect pH levels; however, when levels are
< pH 3 and > pH 11 a dramatic error may occur. This problem is resolved using a built in ATC (Automatic Temperature compensation) which uses a mathematical formula (Nernst equation) to correct pH errors due to temperature factors.

Other factors that affect the life of a sensor Because standard glass electrodes are manufactured using a silver/silver chloride electrode inserted into
a potassium chloride/silver chloride solution, the following list of solutions cause the reference solution to precipitate. If the following solutions are tested, it is recommended that the pH sensor well be thoroughly rinsed. The testing of these solutions will severely reduce the service life of the pH sensor.

1. Heavy metals – silver, iron, and lead
2. Proteins
3. Low ion solutions – distilled water
4. High sodium concentrates
5. Sulfides
6. Fluorides (In high concentrations or prolonged use)

Note: This is not a complete list of solutions that can cause the reference solution to precipitate.

Sodium ion error

As solutions approach, and exceed the pH level of 12.0 the high concentration of sodium ions interfere with the standard glass membrane and cause pH levels to be displayed lower than actual pH levels. If solutions being tested are normally high alkaline, (>12 pH) a probe manufactured with special glass may be required. The special glass may be used throughout the pH range of 0 to 14, but due to the high resistance nature of the glass it will significantly increase the overall time to analyze a sample. Constant use in solutions with pH levels higher than 12 will reduce the life of the probe.

Calibration

The break down of the pH sensor electrodes and the depletion, and/or saturation of the reference solution require your pH instrument to be re-calibrated. This should normally be performed twice a month, but depending on the actual use of the instrument it may be necessary to increase the intervals between calibrations.

Refer to your operations manual or to Myron L Meters video page for detailed instructions on your specific instrument calibration procedures. The calibration should be performed using at least two pH buffer standards. The initial calibration should use Myron L pH buffer solution 7. This will check and allow the instrument to be adjusted so its output reflects 0 millivolts, neutral, or pH 7. A second calibration using a standard solution that reflects the normal range of solutions being analyzed. If acidic solutions are normally tested, a pH buffer solution 4 should be used. If solutions to be tested are normally alkaline, a pH buffer solution 10 should be used. It is not necessary to calibrate your instrument over three standards (4, 7, and 10) unless during normal daily use of the instrument, the solutions being tested varies from low to high pH ranges. In
this case an increase of calibration intervals is also recommended.

How to maximize the life of your pH or pH/ORP sensor

Myron L uses a general-purpose glass pH sensor. This glass sensor may be used in most applications. To ensure maximum life of your Myron L pH test instruments, the following information should be considered whether you are a distributor or an end user. Most premature pH sensor failures can be prevented with a few maintenance procedures. The following procedures should be performed after using your Myron L meter, or if you plan to store your meter for an extended period of time.

1. The pH sensor well (fig 1) must be filled with
Myron L storage solution (preferred) or Myron L pH buffer 4, or tap water with table salt added and its protective cap (with foam insert) firmly installed.
Failure to do so will:
• Allow the glass membrane to dry out. A de- hydrated glass membrane will not produce the necessary “Gel layer” on the sensor surface, which is essential to allow the exchange of hydrogen ions (measure pH).
• Allow airborne contaminants to settle on the glass membrane surface. Once contaminants dry onto the surface of the glass membrane, it will inhibit the transfer of hydrogen ions. (See factory approved cleaning process below.)
• Allow the reference junction to dry out. The reference junction material is usually a wick or fiber type material that completes the electrical circuit between the reference electrode cell
and the solution being tested. Dehydration causes the reference solution to leach out of the electrode cavity, and form crystals in the junction. This is normally referred to as the “Bridging effect”.
Repeated dehydration of the pH or pH/ORP sensor will cause the instrument to have a slower response time, and be more difficult to calibrate. Dehydration will
significantly reduce the normal service life of the sensor.

2. Store spare pH or pH/ORP sensors in a refrigerator. “Do not Freeze”. Take proper precautions not to allow the temperature to fall below freezing. This
will cause the solution to expand and may damage the electrodes inside the sensor. Storage in a refrigerated environment will slow the evaporation of the storage solution, but not prevent evaporation. Always inspect and replace storage solution in spare sensor well on a regular basis.
Note: When using the Myron L storage solution, it is common for white crystal formations to form around the seal of the pH sensor well and protective cap; this is a normal occurrence as the solution evaporates. Never store the sensor in high purity water (distilled or de-ionized).
Approved factory cleaning process

Figure 1

Failure to do so will:
• Allow the glass membrane to dry out. A de- hydrated glass membrane will not produce the necessary “Gel layer” on the sensor surface, which is essential to allow the exchange of hydrogen ions (measure pH).
• Allow airborne contaminants to settle on the glass membrane surface. Once contaminants dry onto the surface of the glass membrane, it will inhibit the transfer of hydrogen ions. (See factory approved cleaning process below.)
• Allow the reference junction to dry out. The reference junction material is usually a wick or fiber type material that completes the electrical circuit between the reference electrode cell
and the solution being tested. Dehydration causes the reference solution to leach out of the electrode cavity, and form crystals in the junction. This is normally referred to as the “Bridging effect”.
Repeated dehydration of the pH or pH/ORP sensor will cause the instrument to have a slower response time, and be more difficult to calibrate. Dehydration will
significantly reduce the normal service life of the sensor.

2. Store spare pH or pH/ORP sensors in a refrigerator. “Do not Freeze”. Take proper precautions not to allow the temperature to fall below freezing. This
will cause the solution to expand and may damage the electrodes inside the sensor. Storage in a refrigerated environment will slow the evaporation of the storage solution, but not prevent evaporation. Always inspect and replace storage solution in spare sensor well on a regular basis.
Note: When using the Myron L storage solution, it is common for white crystal formations to form around the seal of the pH sensor well and protective cap; this is a normal occurrence as the solution evaporates. Never store the sensor in high purity water (distilled or de-ionized).

Approved factory cleaning process for the pH sensor
During normal use of your Myron L handheld pH or pH/ORP meter, you’ll have to clean your pH sensor bulb. The cleaning is necessary because of deposits left on the sensor from the test samples.
If you suspect your instrument is inaccurate, or the display value drifts, or the response is slow and sluggish, try the following.
Rinse the sensor well (three times) and fill with pH buffer 4 solution. If the pH continues to drift below the pH 4 level (i.e. 3, 2, or 1) repeat the test using pH buffer 10. If the pH level drifts beyond the pH level of 10 (i.e. 11, 12 etc.) follow the cleaning procedure outlined below.
If the pH levels of the buffer solutions 4 and 10 actually drift towards pH 7, this could mean that the pH sensor is damaged and needs to be replaced.

Caution: Wear proper eye protection and gloves during the cleaning procedure.

The following procedures may help clean and recover the pH or pH/ORP sensors.

NOTE: Not all pH or pH/ORP sensors can be recovered.
1. Fill the pH/ORP sensor well with 100% Isopropyl alcohol. If not available use additive- free rubbing alcohol (70%). This will remove any oils.
2. Allow the sensor to soak for 10 minutes.
3. Rinse with RO or DI water.
4. Rinse the sensor well (three times) and fill
with Myron L storage solution or Myron L pH buffer 4. Replace the protective cap and allow the sensor to recover overnight.
5. Re-calibrate the instrument according to the Myron L instruction manual that was provided with your instrument. If the instrument fails to calibrate properly, continue to the next step.

If the above procedure does not recover the pH sensor function, perform the following:
1. Fill the pH or pH/ORP sensor well with a hot salt solution 60°C (140°F) potassium chloride (KCI preferred) or hot tap water with table salt (NaCl). Allow the solution to cool.
2. Re-calibrate the instrument according to the Myron L instruction manual that was provided with your instrument. If the instrument fails to calibrate properly, the pH or pH/ORP sensor must be replaced.

Warranty
The manufacturer warrants the pH and pH/ORP sensor assemblies against manufacturer defects. Shelf life for most pH and ORP sensors is 12 months. Failure to maintain proper hydration of the glass pH sensors or the use of the instrument in any manner not described in the operation manual supplied with the instrument may shorten the life of the sensor.
*CAUTION: If you do not use your Myron L instrument on a regular basis or if you are a stocking distributor, the storage solution in the pH or pH/ORP sensor well will evaporate over time and must be replenished. To prevent premature pH glass sensor failure, the manufacturer suggests a preventative maintenance program. Failure to do so could void the factory warranty. The use of liquids containing high levels of solvents, such as acetone, xylene, and chlorinated hydrocarbons, or other harsh chemicals in your Myron L meter is not recommended. Doing so may damage the sensor.

Categories : Care and Maintenance, Technical Tips

Using LSI to preserve an Arizona treatment plant’s distribution systems

Posted by 16 Aug, 2013

Tweet                    The first thing anyone who manages water and wastewater learns is that water is the universal solvent. Because of the unique properties of that dihydrogen monoxide molecule, owing to the extreme electronegativity of the oxygen atom, water is highly polarized and dissolves almost everything with […]

Myron L Ultrameter II 6P

 

 

 

 

 

 

 

 

 

 

The first thing anyone who manages water and wastewater learns is that water is the universal solvent. Because of the unique properties of that dihydrogen monoxide molecule, owing to the extreme electronegativity of the oxygen atom, water is highly polarized and dissolves almost everything with which it comes into contact. This fact is important when one has to maintain equipment and structures that process and distribute water because what the water has dissolved in it can cause it to be corrosive or scaling. What water generally has dissolved in it is at least some carbon dioxide and some calcium carbonate.

Carbon dioxide is ubiquitous and dissolves at the surface of the water, forming carbonic acid in solution. Calcium carbonate, dissolved by the carbonic acid, is globally present in rock formations (limestone), as well as in the physiological structures of organisms (particularly oceanic organisms) that excrete it. Calcium carbonate in its various forms is also used to buffer pH and stabilize solution in process control. Managing the calcium carbonate equilibrium becomes critical to managing any water and wastewater treatment process.

Too little calcium carbonate yields water that is not saturated and may cause corrosion and deteriorate equipment and structures. A supersaturated solution will likely precipitate calcium carbonate, causing scale, reducing efficiency and eventually leading to system failure.

LSI in AZ

One method for analyzing and managing corrosion and scale deposition of water is to use the Langelier Saturation Index (LSI). In Scottsdale, Ariz., Gary Lyons is managing LSI at his water treatment facility using the Myron L Ultrameter II 6P.

His drinking water treatment plant takes 70 million gal per day (mgd) of water from the Central Arizona Project canal and treats it for residential and commercial use. Within the 143-acre campus, the plant processes 20 mgd to of wastewater from the city of Scottsdale collection system using microfiltration and reverse osmosis (RO). Water coming from the RO treatment process is acidic around pH 5.5. It is then moved to decarbonation towers and lime is added to bring the LSI value close to zero. The water reclamation plant features 8 mgd of storage capacity. Recycled water treated by the plant is used for the irrigation of 20 Scottsdale golf courses.

There is great concern about how the water balance will affect this distribution system over time, especially due to higher total dissolved solids values. Plant technicians compute LSI values in the field with the 6Psi hand-held to determine what adjustments should be made and how in real time. The LSI calculator allows them to perform what-if scenarios on changes in pH, alkalinity, hardness and temperature. They are able to measure the effects of changes immediately as well in the facility and at distribution points.

Hardness and alkalinity are variables in the LSI calculation because they account for the availability of calcium in various forms in the water. Variables such as temperature and pH contribute to the likelihood of the formation of calcium carbonate.

The version of the LSI calculation used by the 6Psi LSI calculator is:

LSI = pH + TF + CF + AF – 12.1

In this calculation, pH = the measured value of pH in pH units; TF = 0.0117 x temperature – 0.4116; CF = 0.4341 x ln(Hrd) – 0.3926; and AF = 0.4341 x ln(AL) – 0.0074.

The first thing anyone who manages water and wastewater learns is that water is the universal solvent. Because of the unique properties of that dihydrogen monoxide molecule, owing to the extreme electronegativity of the oxygen atom, water is highly polarized and dissolves almost everything with which it comes into contact. This fact is important when one has to maintain equipment and structures that process and distribute water because what the water has dissolved in it can cause it to be corrosive or scaling. What water generally has dissolved in it is at least some carbon dioxide and some calcium carbonate.

Carbon dioxide is ubiquitous and dissolves at the surface of the water, forming carbonic acid in solution. Calcium carbonate, dissolved by the carbonic acid, is globally present in rock formations (limestone), as well as in the physiological structures of organisms (particularly oceanic organisms) that excrete it. Calcium carbonate in its various forms is also used to buffer pH and stabilize solution in process control. Managing the calcium carbonate equilibrium becomes critical to managing any water and wastewater treatment process.

Too little calcium carbonate yields water that is not saturated and may cause corrosion and deteriorate equipment and structures. A supersaturated solution will likely precipitate calcium carbonate, causing scale, reducing efficiency and eventually leading to system failure.

Indicator Analysis

LSI has been useful as a scaling/corrosion indicator in municipal water treatment for more than 70 years. The original Langelier Saturation (or Stability) Index calculation was developed by Dr. Wilfred Langelier in 1936 to be used as a tool to develop strategies to counteract corrosion of plumbing in municipal water distribution systems. It is a statement about the change in pH required to bring the calcium carbonate in water to equilibrium. LSI is a measure of the disparity between the pH of the system and the pH at which the system is saturated with calcium carbonate: LSI = pH – pH of saturation.

As such, the LSI indicates the change in pH required to bring water to equilibrium. If the LSI is +1, then the pH needs to be lowered by one unit to bring the water to equilibrium. If the LSI is -1, the pH needs to be raised by one unit to bring the water to equilibrium.

A positive saturation index means that the pH of the water is above equilibrium. The water is scaling because as pH increases, total alkalinity concentration increases. This is due to an increase in the carbonate ion, which bonds with calcium ions present in solution to form calcium carbonate (reference the carbonic acid equilibrium, in which hydrogen ions bond with carbonate ions to form bicarbonate and hydrogen ions bond with bicarbonate to form carbonic acid). Thus, any positive value for LSI is scaling.

If the pH is less than the pH of saturation, the index will be negative, which is corrosive. This means that the water is more acidic than it would be at equilibrium. There are less carbonate ions present, according to the carbonic acid equilibrium. The water will be aggressive because it has room for more ions in solution. Thus, any negative value for LSI indicates that the water may tend to be corrosive.

The use of LSI as an indicator is well documented and time-tested. Managing water balance through LSI analysis will prevent loss of efficiency and failure of equipment and structures, saving time and money.

Myron L Meters is the premier online internet retailer of the Myron L Ultrameter II 6P.  Find out more about the Ultrameter II 6P here:

https://www.myronlmeters.com/Myron-L-6P-Ultrameter-II-Multiparameter-Meter-p/dh-umii-6pii.htm

Categories : Application Advice, Case Studies & Application Stories, Technical Tips

Using the Ultrameter II 6P in a Power Plant

Posted by 16 Aug, 2013

TweetFind out how a plant chemistry and O&M technician with 18 years experience, uses the Ultrameter II 6P to optimize blowdowns and control corrosion, scale, contamination & chemicals Deborah Walker, an operation and maintenance technician and plant chemistry technician in manufacturing and energy production has been managing water quality in industrial processes for more than […]

The Ultrameter II 6P

The Ultrameter II 6P

Find out how a plant chemistry and O&M technician with 18 years experience, uses the Ultrameter II 6P to optimize blowdowns and control corrosion, scale, contamination & chemicals

Deborah Walker, an operation and maintenance technician and plant chemistry technician in manufacturing and energy production has been managing water quality in industrial processes for more than 18 years. Through her extensive experience, she has come to rely on the Myron L Ultrameter II as a way to monitor control parameters that ensure the functioning of automatic controllers and chemical dosers that optimize cooling tower blowdown schedules; prevent scale, corrosion and microbiological fouling; screen influent and effluent for process parameter control and environmental compliance; as well as directly measuring parameters critical to a total quality assurance plan.

Deborah’s most recent use of the Ultrameter II 6P  was in a high output power plant implementing a Heat Recovery Steam Generator (HRSG), gas and steam turbines, all required heat exchangers, cooling towers, and chemical controllers that preserved the life of the equipment and structures in the water circulation loop while minimizing water and energy consumption. Deborah used the UMII as part of quality assurance for all water and steam quality. Make up water for this application was sourced from a massive municipal pipeline with wastewater being discharged into a nearby creek.

Much of the online controllers Deborah monitored featured an online sampling panel. Deborah used the Ultrameter II to draw solution from the panel to ensure the online meters that monitored cooling water throughout the system were functioning properly. Because the Ultrameter II 6P  measured all of the parameters critical to her operation, including conductivity, pH, ORP and temperature, she was able to efficiently analyze equipment functioning and chemical dosing quickly and accurately.

The Ultrameter II 6P also features data logging with memory for up to 100 readings, eliminating the need to perform record keeping tasks in the field. This means Deborah could monitor more areas of the plant in less time. Chemicals injected into the system included a cooling water dispersant that consisted of sodium bisulfate and sodium formaldehyde bisulfite. Sodium bisulfate effectively lowered the pH of the system and sodium formaldehyde bisulfite also served as an oxygen scavenger. (Removing oxygen from the system helps to prevent the formation of the hydroxide ion and hence the formation of rust, disrupting the processes of the corrosion cell. Tetrapotassium pyrophosphate is used for water stabilization and disrupts the corrosion process at the cathodic areas by combining with calcium or iron to form a complex film.) pH monitoring with the Ultrameter II 6P was required to ensure target levels as well as optimum chemical performance.

Deborah also used the Ultrameter II 6P as a quality check to maintain the HRSG. To do this, she tested the purity of the steam by measuring conductivity of steam at the sample panel for boiler chemistry control.

The steam that issued from the HRSG to the turbine had the potential to errode or deposit, which could affect energy efficiency, as well as damage equipment. Any deposits would add mass to the turbine, making it more difficult to turn with greater friction, requiring more energy for the mass with more energy lost as heat. Any increase in conductivity in the steam indicated that either something undesirable was in the water as it was coming in or that there was something wrong with the combustion chemistry—either the dirty water was carried over to the steam or the steam was eroding the boiler and picking up minerals from the metal components. If the steam was corrosive, preventative corrections could be made to stem any equipment damage. If other chemical contamination was evident, additional pretreatment and other chemical controls could be implemented.

Using the Ultrameter II 6P for steam quality control not only increased HRSG energy efficiency and equipment lifecycle, but also decreased its environmental footprint because some of the chemical contaminants that could form deposits could only be removed by other dangerous chemicals with extensive outage during maintenance. The operational target for specific conductivity blowdown identified by Deborah with the Ultrameter II was 1200-1400µS with a goal of 10 cycles of concentration.

Deborah also used the Ultrameter II as part of a disinfection program. Chlorine was used to mitigate biological fouling and corrosion. Chlorine injection occurred at 8 a.m. and 2 p.m. with blowdowns scheduled for once at night and once during the day. Deborah’s target residual level range for system disinfection was 0.2-0.6 ppm free chlorine. The bleach injection used in disinfection, however, not only interfered directly with pH control, but also with the effectiveness of other chemicals used to prevent scaling and corrosion.

Chlorine also had to be kept at a consistent reasonable level at all times to avoid shocking the system with massive doses, which could make the system erratic and difficult to balance. During a shock, biological growth could come loose as well, potentially clogging membranes or small pipes in the sample panel. Spot checking parameters such as pH, ORP and conductivity with the Ultrameter II was critical to ensuring consistent residual chlorine levels, pH, and scale and corrosion inhibitors between blowdowns.

The Ultrameter II 6Pwas used by Deborah to verify the accuracy of monitors that controlled demineralizer water used in other processes at the power plant. Three trains were employed to remove dissolved solids. The first vessel removed cations. The second vessel removed anions. The third was a mixed bed that removed both types. The Ultrameter II 6P  could be used to determine when the trains had become saturated and needed to be regenerated by measuring any increase in conductivity downstream from the beds. Acid injection was used to flush the demineralizer out, which was then rinsed. Deborah used the Ultrameter II to ensure that the brine wastewater that resulted was neutralized and documented its pH and conductivity before it was shipped away.

Deborah also had to mitigate the environmental impact of discharged cooling waters. She used the Ultrameter II 6P  to take measurements of pH and temperature of the water from a creek upstream of the plant to establish a baseline for compliance for the wastewater, so that she could get the water as close to the natural conditions of the creek as possible before discharge.

The chlorine injected to kill microbes and prevent fouling while the cooling water was being recirculated also had to be removed from the water before it entered the creek. This is because the chlorine could also kill desirable organisms important to the ecosystem of the creek, either by direct oxidation or accumulation to toxic levels in living tissues. If chlorine residual was above 0.2 ppm, the waste stream was diverted to sodium bisulfite skids. On the discharge side of the skids, Deborah used the Ultrameter II to test that sodium bisulfite was injected and effective at binding with and deactivating the chlorine by measuring the Oxidation Reduction Potential (ORP). ORP measured the total killing power of all sanitizers in solution by measuring the chemical activity, rather than any specific constituent. Deborah also checked the free chlorine level again specifically.

The sodium bisulfite skid itself also caused the pH of the water to vary slightly. So Deborah made a final check of the pH using the Ultrameter II. The pH was controlled to between 6.6 and 8.6 to optimize the efficacy of other chemicals in solution. The cooling tower would typically blow down within this range, but could be as high as the administrative limit, which was set at 8.7—still well within permit discharge limits, but only with special permission.

The outside blowdown line from the cooling tower dumped into a settling basin before it traveled out to the creek. Deborah used the Ultrameter II  6P to test conductivity, pH, ORP and free chlorine before the cooling water was discharged into the settling basin to ensure compliance with the established guidelines.

Part of effluent compliance also included a plan to monitor and control stormwater runoff from the plant. Deborah used the Ultrameter II 6P to monitor and report pH and conductivity following a major rain event.

Ranges for other operational limits include 80-130 mg/L (ppm) Ca, which usually runs at about 60 mg/L; 0-0.5 mg/L iron, which usually runs at about 0.30 mg/L; microorganism plate count of 0-104 cfu/mL, and suspended solids between 0-25 mg/L.

Deborah has also used the Ultrameter II 6P as part of a Quality Assurance plan for a prominent electric semiconductor manufacturer in which she used conductivity measurements to ensure semiconductor chip quality through proper rinsing.

Myron L Meters is the premier online internet retailer of the Myron L Ultrameter II 6P.  Find out more about the Ultrameter II 6P here:

https://www.myronlmeters.com/Myron-L-6P-Ultrameter-II-Multiparameter-Meter-p/dh-umii-6pii.htm

Categories : Application Advice, Case Studies & Application Stories, MyronLMeters.com Valued Customers, Technical Tips

Water Quality Testing in RO Systems – MyronLMeters.com

Posted by 10 May, 2013

Tweet Water quality testing is vital to the design of an efficient, cost-effective RO system, and is one of the best ways to preserve system life and performance. Using an accurate Total Dissolved Solids (TDS) measurement to assess the system load prevents costly mistakes up front. The TDS measurement gives users the information they need […]

DH-UMIII-9PTK-2T

Water quality testing is vital to the design of an efficient, cost-effective RO system, and is one of the best ways to preserve system life and performance.

Using an accurate Total Dissolved Solids (TDS) measurement to assess the system load prevents costly mistakes up front. The TDS measurement gives users the information they need to determine whether or not pretreatment is required and the type of membrane/s to select. Ultrameter™ and ULTRAPEN PT1™ Series TDS instruments feature the unique ability to select from 3 industry standard solution models: 442 Natural Water™ NaCl; and KCl. Choosing the model that most closely matches the characteristics of source water yields measurements accurate enough to check and calibrate TDS monitor/controllers that can help alert to system failures, reducing downtime and increasing productivity. The same instruments provide a fast and accurate test for permeate TDS quality control. Measuring concentrate values and analyzing quality trends lets users accurately determine membrane usage according to the manufacturer’s specifications so they can budget consumption correctly. These daily measurements are invaluable in detecting problems with system performance where changes in the ionic concentration of post-filtration streams can indicate scaling or fouling. System maintenance is generally indicated if there is either a 10-15% drop in performance or permeate quality as measured by TDS.

Thin-film composite membranes degrade when exposed to chlorine. In systems where chlorine is used for microbiological control, the chlorine is usually removed by carbon adsorption or sodium bisulfite addition before membrane filtration. The presence of any chlorine in such systems will at best reduce the life of the membrane, thus, a target of 0 ppm free chlorine in the feedwater is desirable.

ORP gives the operator the total picture of all chemicals in solution that have oxidizing or reducing potential including chlorine, bromine, chloramines, chlorine dioxide, peracetic acid, iodine, ozone, etc. However, ORP can be used to monitor and control free chlorine in systems where chlorine is the only sanitizer used. ORP over +300 mV is generally considered undesirable for membranes. Check manufacturer’s specifications for tolerable ORP levels.

An inline ORP monitor/controller placed ahead of the RO unit to automatically monitor for trends and breakthroughs coupled with spot checks by a portable instrument will prevent equipment damage and failure. Myron L 720 Series II™ ORP monitor/controllers can be configured with bleed and feed switches as well as visible and audible alarms.

Ultrameter and ULTRAPEN portable handhelds are designed for fast field testing and are accurate enough to calibrate monitor/controllers. Our measurement methods are objective and have superior accuracy and convenience when compared to colorimetric methods where determination of equivalence points is subjective and can be skewed by colored or turbid solutions.

Monitoring pH of the source water will allow users to make adjustments that optimize the performance of antiscalants, corrosion inhibitors and anti-foulants. Using a 720 II Series Monitor/controller to maintain pH along with an Ultrameter Series or ULTRAPEN PT2™ handheld to spot check pH values will reduce consumption of costly chemicals and ensure their efficacy.

Most antiscalants used in chemical system maintenance specify a Langelier Saturation Index maximum value. Some chemical manufacturers and control systems develop their own proprietary methods for determining a saturation index based on solubility constants in a defined system. However, LSI is still used as the predominant scaling indicator because calcium carbonate is present in most water. Using a portable Ultrameter III 9PTKA™ provides a simple method for determining LSI to ensure the chemical matches the application.

The Ultrameter III 9PTKA computes LSI from independent titrations of alkalinity and hardness along with electrometric measurements of pH and temperature. Using the 9PTKA LSI calculator, alterations to the water chemistry can be determined to achieve the desired LSI. Usually, pH is the most practical adjustment. If above 7, acid additions are made to achieve the pH value in the target LSI. Injections are made well ahead of the RO unit to ensure proper mixing and avoid pH hotspots. A Myron L 720 Series II pH Monitor/controller will automatically detect and divert solution with pH outside the range of tolerance for the RO unit. ULTRAPEN PT2, TechPro II and Ultrameter Series instruments can be used to spot check and calibrate the monitor/controller as part of routine maintenance and to ensure uniform mixing.

Water hardness values indicate whether or not ion exchange beds are required in pretreatment. Checking hardness values directly after the softening process with the Ultrameter III 9PTKA ensures proper functioning and anticipates the regeneration schedule.

Alkalinity is not only important in its effect on the scaling tendency of solution, but on pH maintenance. Additions of lime are used to buffer pH during acid injection. Use a 9PTKA to measure alkalinity values for fast field analysis where other instrumentation is too cumbersome to be practical.

Though testing and monitoring pressure is a good way to evaluate system requirements and performance over time, measuring other water quality parameters can help pinpoint problems when troubleshooting. For example, if the pressure differential increases over the second stage, the most likely cause is scaling by insoluble salts. This means that any degradation in performance is likely due to the dissolved solids in the feed. Using a 9PTKA to evaluate LSI and calculate parameter adjustments is a simple way to troubleshoot a costly problem.

Myron L Meters saves you 10% on all Ultrameters and Ultrapens when you order online at MyronLMeters.com, where you can find the complete selection of Myron L meters, including the Ultrameter III 9PTKA.

Original story from International Filtration News V 32, no. 2

 

Categories : Application Advice, Case Studies & Application Stories, Technical Tips

Testing Hydroponics System’s Nutrient Solution – MyronLMeters.com

Posted by 3 Apr, 2013

TweetTDS meter Whether or not you’re a newcomer to hydroponic growing, keeping your hydroponic system’s nutrient solution properly balanced with a satisfactory nutrient concentration can be tough. Regular testing of one’s t solution is required if you want to keep the hydroponic system balanced and your plants healthy and growing. The simplest way to keep […]

TDS meter

Whether or not you’re a newcomer to hydroponic growing, keeping your hydroponic system’s nutrient solution properly balanced with a satisfactory nutrient concentration can be tough. Regular testing of one’s t solution is required if you want to keep the hydroponic system balanced and your plants healthy and growing. The simplest way to keep your nutrient solution balanced is via testing. You must check your solution’s pH level and nutrient concentration no less than every couple of days. To be able to try out your solution you need a few basic devices. You need to get a trusted pH tester and either an overall total Dissolved Solids (TDS) meter or perhaps a Conductivity (EC) meter.

pH tester

It is generally agreed that the pH of one’s nutrient solution should be kept slightly acidic using a pH range of 5.5-6.0. You will find exceptions for this generalization. If you are unsure what are the best pH range is for the plants you might be growing, there are many resources open to guide you. You can find three basic means of testing pH. The least expensive technique is paper testing strips. They’re simple to use but could be difficult to learn. Typically the most popular testing way is liquid test kits. This method is extremely accurate and easier to see than paper testing strips but it is also more expensive. An electronic digital pH meter may be the last available option. Digital pH meters are available in various shapes, sizes, and price ranges. The benefit of an electronic pH meter is that it can be really user friendly, fast, and accurate. However, they are the most costly of the testing options, they can break easily, plus they has to be calibrated frequently if you’d like them to remain accurate.

TDS tester

Both conductivity meters and TDS meters are used to look at the strength, or concentration, of your hydroponic nutrient solution. Even though it is crucial that you know the concentration of your solution, this is because measurements ought to be used being a guideline only. EC meters will almost always be measured much the same way. Two sensors they fit within the solution being tested along with a little bit of electricity is emitted by one sensor and received by the other sensor. How well the electricity travels is then based on the EC meter. The harder electricity conducted, the greater the power of solids in the solution. A TDS meter uses the EC after which calculates the amount of solids inside the solution according to among three conversion factors. Considering that the TDS is dependant on a calculation, it really is only a quote of solids in the nutrient solution.

With this particular basic comprehension of the main difference between TDS and conductivity meters you can determine which measurement process is best for you. When you use a packaged nutrient solution, browse the product label to learn which kind of meter the maker recommends. In the event the manufacturer recommends a TDS, they’ll also inform you which conversion step to use as well as the recommended concentration range for his or her product. If you use a homemade nutrient solution plus a TDS meter, a great general guideline is to keep your TDS between 800 and 1200 ppm (ppm). If you work with an EC meter to test your homemade nutrient solution, a good range is 1.0 to 3.0 mS/cm (milisiemens per centimeter).

This information will help keep your hydroponics nutrient solution balanced and your plants healthy.

Myron L Meters has the perfect solution for hydroponics testing – the Ultrapen Combo.

ULTRACOMBO – ULTRAPEN PT1  Conductivity – TDS – Salinity pen & PT2  - pH – Temp Pen

Accuracy of +/-1% of READING (+/-.2% at Calibration Point)
Accuracy of +/- 0.01 pH
Reliable Repeatable Results
Solution modes: KCl, NaCl and 442
Automatic Temperature Compensation
Autoranging
Durable, Fully Potted Circuitry
Comes with 2oz bottle of pH Storage Solution
Waterproof

Ultrapen Combo

List Price: $318.00 

Exclusive Online Price: $280.50

http://www.myronlmeters.com

 

 

 

 

 

 

 

Material Shared via Creative Commons Attribution-Share Alike 2.5 Croatia, original found here: http://blog.dnevnik.hr/nathanielwhite566668/2012/02/1629933596/tds-meter.html

 

 

 

 

Categories : Application Advice, Case Studies & Application Stories, Technical Tips